This is widely naturalized across northern states. In Ky. the first records date from the 1950s. A few plants were initially identified as G. rotundifolium L. (Gunn 1968). These two species plus pusillum are closely related weeds (2n = 26), with ecological differences poorly understood, but hybrids are not documented. Another potential segregate is G. molle var. aequale Babington, which is distinguished by the lack of reticulate ridges on mericarps (versus present in typical molle), seeds more or less smooth (versus striate), and petals mostly 3.5-4.5 mm long (versus 4.5-8.5 mm). Aedo (2012) elevated this taxon to species status and reported it from Ky., but details are not yet available (W).